1. Field of the Invention
There is a continuing need for polymeric materials exhibiting a retention of physical properties and exhibiting continued strength and toughness over a wide temperature range. This invention relates to crosslinked aromatic polyimide polymeric materials with such qualities. This invention more particularly pertains to such aromatic polyimide polymeric materials made as a crosslinked chemical combination of at least two precursor polyimide resins of certain kind and in certain amount.
As a particular example of one use to which the crosslinked aromatic polyimide is put, this invention also relates to molded, filled articles wherein the crosslinked polyimide is a matrix or binder material for filler particles. More particularly, this invention pertains to such filled articles wherein abrasive filler particles are held by the crosslinked polyimide to yield high speed grinding wheels especially suited for dry grinding operations.
2. Discussion of the Prior Art
Crosslinked polyimide materials are disclosed in U.S. Pat. No. 3,533,997 issued Oct. 13, 1970 on the application of Angelo. Crosslinking is accomplished in those polyimide materials by reacting polyimide polymers with relatively simple polyamine crosslinking compounds. The polyamine crosslinking compounds are disclosed to have a maximum of twenty carbon atoms and polymeric polyamines are not disclosed.
U.S. Pat. No. 3,632,554 issued Jan. 4, 1972 on the application of Kubota discloses a heat resistant polyimide. The polyimide disclosed therein is prepared from two oligomers: one having terminal pairs of carboxyl groups and the other having terminal amine groups. The reaction is between an amine end group and an end group including a pair of carboxyl groups or derivatives of carboxyl groups and the product of the reaction is a linear polyimide.
U.S. Pat. No. 3,897,395 issued July 29, 1975, on the application of D'Alelio discloses the preparation of aromatic polyimide materials using equivalent amounts of oligomeric polyimides. That patent also teaches preparing a mixture including a one-fold molar excess of one of the oligomeric polyimides as a crosslinking agent and then heating the mixture at a temperature of about 300.degree. centigrade.
U.S. Pat. No. 3,179,631 issued Apr. 20, 1965 on the application of Endrey; U.S. Pat. No. 3,718,447 issued Feb. 27, 1973 on the application of Hibbs et al.; and British Pat. No. 1,263,234 published Feb. 9, 1972, all disclose polyimide polymeric materials used as binders for abrasive articles. U.S. Pat. No. 3,179,631 discloses a single, linear, polyimide material prepared from dianhydride and diamine monomers without crosslinking. U.S. Pat. No. 3,718,447 discloses the use of a single thermosetting polyimide prepolymer material which undergoes crosslinking through the action of aliphatically unsaturated imide groups included in the prepolymer. British Pat. No. 1,263,234 discloses a polyimide binder made from a single prepolymer material.